Shareholders' Equity - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	$ 3,898,666
Shareholders' equity, ending balance	4,759,552
Available- for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	7,048	$ 4,484
Other comprehensive income before reclassifications	148	1,485
Amounts reclassified from accumulated other comprehensive income	(884)	68
Net current-period other comprehensive income (loss)	(736)	1,553
Shareholders' equity, ending balance	6,312	6,037
Cash Flow Hedges | Interest rate agreements
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	(112,302)	(187,524)
Other comprehensive income before reclassifications	28,315	76,602
Amounts reclassified from accumulated other comprehensive income	1,294	286
Net current-period other comprehensive income (loss)	29,609	76,888
Shareholders' equity, ending balance	(82,693)	(110,636)
Cash Flow Hedges | Commodity contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance		(4,982)
Other comprehensive income before reclassifications		9,847
Amounts reclassified from accumulated other comprehensive income		(4,865)
Net current-period other comprehensive income (loss)		4,982
Shareholders' equity, ending balance		0
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	(105,254)	(188,022)
Other comprehensive income before reclassifications	28,463	87,934
Amounts reclassified from accumulated other comprehensive income	410	(4,511)
Net current-period other comprehensive income (loss)	28,873	83,423
Shareholders' equity, ending balance	$ (76,381)	$ (104,599)